Deposition of Ohmic Contacts on NanoLEDs Devices By Surface
Cleaning
Elizabeth Avelar Mercado1, Seth Fortuna2, Prof. Ming C. Wu2
1Merced
College, 2University of California Berkeley
2014 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU Program)
Abstract.- NanoLEDs are seen as a possible light source components of optical interconnects in the replacement of electrical interconnects.
However, many problems have to be solved for this to become a reality. NanoLEDs suffer from a high contact resistance (~10-4 ohm-cm2). This is
detrimental to the device performance and reliability because of the excess heat generated from the large voltage drop due to the series
resistance. Native oxide on InP surface is considered to be one of the factors that contribute to the high contact resistance since it works as an
insulator, which makes it really hard for the device to conduct current. In this experiment, Transfer Length Method (TLM) test structures were
fabricated. The native oxide on some of the structures was removed by the application of different compositions of HCL and H2SO4 while other
structures were left untreated with the purpose of comparison of final results. Contact resistivity, Pc, was extracted from the samples afterwards.
The results are analyzed, and the optimum cleaning method is discussed.
1. Motivation
3. Methods
In modern integrated circuits, about 50% to 80% of the power is lost
through the copper interconnects that electrically connect transistors. For
this reason, there is a strong push to replace copper interconnects by
optical interconnects because they are faster and more efficient.
Optical
antenna
NanoLED
Two Processes of fabrication
•Process 1, Chemicals Tested:
•2 M HCL for 5 min
•HCL + (NH4)2S
•No treatment
•2 H2SO4 for 5 min
•Process 2,
Chemicals
Tested:
•2 M HCL for
5 min
•No treatment
N-InP
1
Substrate
Application
Treatment
of O2
application
plasma by
etch back
N-InP
process
2
Substrate
Application of O2
Plasma
Remove Al3O2
N-InP
N-InP
Substrate
Substrate
Substrate
2
2 M H2SO4 for 5 min
Shottky Diode behavior/ Rt
couldn’t be obtained.
2 M HCL for 5 min
2.0 x 10-5 Ω-cm2
HCL + (NH4)2S
1.43x 10-5 Ω-cm2
No Treatment
Shottky Diode behavior/ Rt
couldn’t be obtained.
Workability
Six structures were
fabricated. One for
every treatment.
•HCL contains higher solubility rates of the oxides compared to H2SO4
•HCL etched about 1 nm of the InP Surface. Not too bad for a strong chemical.
•A higher concentration of H2SO4 was likely needed to observe better results.
•A better contact surface was achieved.
•Since Pc for “HCL” and “Al3O2 + no treatment” resulted in the same order of
magnitude, which is about 10-5 Ω-cm2, it can be concluded that native oxide isn’t
that factor contributing to high contact resistance. Contaminants formed during the
process of fabrication, such as the application of O2 plasma etch back process
might be oxidizing the device, or other contaminants were formed on the surface
after the treatment.
•As future work, wet etch processes will be applied to actual nanoLEDs devices for
the removal of surfaces contaminates. Process of fabrication will be studied as well.
i-InGaAsP
P-Type InP-(5X1018 cm-3)
E3S
Center
Support Information
This work was funded by
National Science Foundation
Awards ECCS-0939514
& EEC-1157089.
Once the
structures
are
fabricated
measure
contact
resistivity,
P c.
Procedure to extrant Pc.
Apply a voltage between
contact pads in a row, by
using a semiconductor
parameter analyzer and a
probe station. Measure
current.
 Probe Station
Semiconductor
Parameter
Analyzer HP
4145b
-+
Acknowledgments
Contact Information
[email protected]
Merced College, Merced Ca, 95301
N-InP-(1X1019 cm-3)
SI-InP
5. Conclusion and Future Work
I would like to thanks my mentor Seth Fortuna for his support and guidance on this project, and to the
for the opportunity given to conduct research.
N-InP-(5X1019 cm-3)
P-Type InGaAsP-(1X1019 cm-3)
10-5 Ω-cm2
1.45 x 10-5 Ω-cm2
Substrate
4
Substrate
Contact Resistivity, Pc
Al3O2 layer + No Treatment
N-InP
Carrier
concentration
Final
structure
with TLM
structures
in it.
4. Results
2.30x
Deposit contact
pads
Ge/Au
•Remove native oxide from InP surface by wet etch processes.
•Chemicals’ etching rate must not degrade the device to any extent.
•Reduce contact resistivity, Pc, by depositing ohmic contacts.
Al3O2 layer + HCL
Substrate
3
2. Objectives
Treatment
N-InP
3
Treatment
application
N-InP
1
Deposit metal
contact
Prob Tips
•Obtain an IV curve for every
space in a row.
•Obtain total resistance, Rt for
every IV curve. Graph Rt Vs.
distance.
•Obtain Rt when D = 0.
•Obtain Pc from:
Rt = 2(
).